As a support for a lithographic printing plate, an aluminum plate or an aluminum alloy plate (hereinafter, those are referred to as "aluminum plate") has hitherto been widely used.
To use the aluminum plate as the support for a lithographic printing plate, it is necessary that the aluminum plate has a proper adhesive property with a photosensitive material and a water-holding property and further is uniformly grained. In this case, the term "uniformly grained" means that the sizes of the pits formed are properly uniform and such pits are uniformly distributed on the whole surface.
Also, the pits give remarkable influences on the scumming, which is the printing impression of a printing plate, and the printing impression and the quality thereof are an important factor for producing printing plates.
As the graining method of an aluminum plate, there are a mechanical graining treatment, a chemical etching treatment, an electrochemical (or electrolytic) graining treatment, etc. For example, JP-A-6-2146 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describes a method of specifying various conditions in the mechanical graining treatment, the chemical etching treatment, and the electrochemical graining treatment. According to the above-described patent publication, it is proposed that after a mechanical graining treatment to an aluminum plate, a chemical etching treatment is applied to the aluminum plate such that the etched amount becomes from 0.5 to 30 g/m.sup.2, an electrochemical graining treatment is applied to the aluminum plate at a proper current density and quantity of electricity, a chemical etching treatment is applied thereto in the range of the etched amount of from 0.1 to 10 g/m.sup.2 to smoothly finish the corners of the unevenness formed in electrochemical graining of the previous step, and an anodic oxidation treatment is applied.
JP-A-7-137474 describes a brush suitable for a mechanical graining treatment.
JP-A-8-132751 describes an aluminum support which is subjected to graining treatments, a desmutting treatment, and an anodic oxidation treatment.
However, these supports for lithographic printing plates described above have a less water-holding amount and are liable to form ink staining and, in particular, to form stains at dot portions. Also, because these aluminum supports have a less water-holding amount, there are disadvantages that the surface of the printing plate is liable to shine, it is difficult to see water result at printing, and the control of water scale is difficult.
As described above, in conventional lithographic printing plates, there is a problem about the handling property in addition to the printing impression, and the further improvement of the scumming of a blanket and the printing impression has been required.